1. Field of the Invention
The present invention broadly relates to an electrophotographic apparatus and, more particularly, to a developing method for developing images on an electrophotographic film in the electrophotographic apparatus.
2. Description of the Related Art
Electrophotographic apparatus has been known in which an image is recorded in a predetermined frame of an electrophotographic film in such a manner that the recorded image can be projected or copied as desired.
The electrophotographic apparatus of the kind mentioned above employs a processing head adapted for conducting various types of processing such as charging/exposure and development on the electrophotographic film. Examples of such a processing head is disclosed in U.S. Pat. Nos. 4,591,543, 4,600,291, 4,622,915, 4,623,240, 4,624,554 and so on.
The processing head disclosed in the above-mentioned publications has a charging/exposure section, a developing section, a drying section and a fixing section which are arranged in series in the mentioned order along the path of feed of the electrophotographic film, at a pitch or interval which corresponds to the pitch of frames on the electrophotographic film.
In the charging/exposure section, the portion of the electrophotographic film located in this section, constituting one frame, is charged and then exposed to an image light from an original, so that an electrostatic latent image corresponding to the pattern of an image carried by the original is formed in this portion of the film. The film is then fed so as to bring the exposed frame to the developing section where a liquid developer is applied to the electrophotographic film so as to develop the latent image thereby making it visible. Subsequently, the frame is brought to the drying section where drying air is blown to the electrophotographic film wetted by the liquid developer, so as to remove moisture component from the film. Finally, the frame is brought to the fixing section where the developed image is fixed to the electrophotographic film by means of, for example, a fixing lamp. The whole system of the aforesaid electrophotographic apparatus and a method of recording and retrieval of an image frame are disclosed in U.S. Pat. No. 4,671,648.
In order to sufficiently and uniformly apply the developer to the whole area of the exposed portion of the electrophotographic film, the developing section usually employs a system which applies a certain level of pressure to the developer. It is also a common measure to supply pressurized air to get rid of any surplus developing agent after the supply of the same. In some cases, a control of the pressure of the air is conducted such that, in the beginning period of supply of pressurized air, the air pressure is kept comparatively low so as not to cause the developer to be exfoliated from the electrophotographic film but is elevated in the later period.
The described known technique encounters the following problems. Namely, the supply of the pressurized air tends to cause any portion of the liquid developer stagnant in and attaching to various portions of the developing chamber to drip onto the image, thereby degrading the developed image due to so-called "drag". Even when the supply of the pressurized air is not conducted, inferior development may result from formation of bubbles in the developer caused by inclusion of air which tends to be introduced into the developer due to incorrect timing of operation of a solenoid valve which is used for the control of supply of the developer. Furthermore, dripping of the liquid developer and bubbling in the same tend to hamper the sensing operation of a sensor which controls the feed of the film.